Pope Francis celebrated his first Palm Sunday Mass in St Peter's Square today, encouraging people to be humble and young at heart, as tens of thousands joyfully waved olive branches and palm fronds.

The square overflowed with some 250,000 pilgrims, tourists and Romans eager to join the new pope at the start of solemn Holy Week ceremonies, which lead up to Easter.

Keeping with his spontaneous style, the first pope from Latin America broke away several times from the text of his prepared homily to
encourage the faithful to lead simple lives.

Palm Sunday recalls Jesus' entry into Jerusalem but its Gospel also recounts how he was betrayed by one of his apostles and ultimately sentenced to death on a cross.

Recalling the triumphant welcome into Jerusalem, Francis said Jesus "awakened so many hopes in the heart, above all among humble, simple, poor, forgotten people, those who don't matter in the eyes of the world".

Francis then told an off-the-cuff story from his childhood in Argentina.

"My grandmother used to say, 'children, burial shrouds don't have' pockets"' the pope said, in a variation of "you can't take it with
you".

Since his election on March 13, Francis has put the downtrodden and poor at the centre of his mission as pope, keeping with the priorities of his Jesuit tradition. His name - the first time a pope has
called himself Francis - is inspired by St Francis of Assisi, who renounced a life of high-living for austere poverty and simplicity to preach Jesus' message to the poor.

Francis wore bright red robes over a white cassock as he presided
over the Mass at an altar sheltered by a white canopy on the steps of St Peter's Basilica.

Cardinals, many of them among the electors who chose him to be the Roman Catholic church's first Latin American pope, sat on chairs during the ceremony held under hazy skies on a breezy day.

In his homily, Francis said Christian joy "isn't born from possessing a lot of things but from having met" Jesus. That same joy should keep people young, he said.

"From seven to 70, the heart doesn't age" if one is inspired by Christian joy, said the 76-year-old pontiff.

Francis said he was joyfully looking forward to welcoming young people to Rio de Janiero in July for the Catholic Church's World Youth Day. So far, that is the first foreign trip on the calendar of Francis' new papacy.

The faithful knelt on hard cobblestones paving the square, and Francis knelt on a wooden kneeler at the point in the Gospel that recounts the moment of Jesus' death.